Question

I am creating a simple chat module where there are two levels.

1. Inbox
2. Conversation

in the Inbox i want to list the conversation between me and other users and display the latest chat message from that particular user.

messages(id, user_id, receiver_id, message, timestamp)

Dummy data

1, 1, 2, "hi there", today

2, 1, 4, "Hey Tommy", yesterday

3, 1, 2, "Wanna meet tonite?", now

Now when i display the list i want to just display two messages
one with user id – 4 and user id 2. But the latest message of userid 2 should be displayed only.

How to do a query where i can get only the latest row from a particular user ?

Answer 1

This is beleive is an efficient way to acheive this:

SELECT M1.* FROM Messages M1 LEFT JOIN Messages M2 
ON M1.ReceiverID = M2.ReceiverID AND M1.Timestamp < M2.Timestamp
WHERE M2.ID IS NULL